STLD41PUR datasheet(10/19 Pages) STMICROELECTRONICS

10 / 19 page

Selection of external components

STLD41

10/19

Doc ID 022283 Rev 5

7.4

RSENSE value

RSENSE = VREF1 / ILED

If using a typical setting of ILED = 120 mA, VREF1 = 160 mV, and RSENSE = 1.3 Ω, the resistor

must be rated for a power dissipation of 1.3 x 0.12² W = 0.02 W.

7.5

PCB layout

Because the STLD41 is a powerful switched device, the PCB must be designed in line with

rules for designing switched supplies. It is recommended to use a two-layer PCB. The power

wirings must be as short as possible and wide. Place all external components close to the

STLD41 device. High-energy switched loops should be as small as possible to reduce EMI.

Most LEDs need cooling, which can be attained utilizing a defined copper area on the PCB.

Use the reference guide for each LED to design the heatsink. Place the RSENSE resistor as

close as possible to pin 2 and ground of the system. The ground of the system is

represented by the size of the area created by the connections GND-PGDN-GNDCIN-

GNDCOUT. When a change of PCB layer is needed, use sufficient vias. During routing, the

PCB must be focused on the minimum area of the application ground; the smaller the

ground area of the DC-DC converter(a), the better the stability and there will be fewer noise

issues. It is recommended to place the copper plate connected through the vias to the

exposed pad to the bottom layer to create the heatsink of the device.

The application ground area is represented by the area which is created by the ground pins of the CIN, COUT,

and ground of the DEVICE and GND connection of the load.

STLD41PUR Datasheet(PDF) 10 Page - STMicroelectronics